A prostaglandin is a physiologically active substance that is synthesized from an essential fatty acid having 3 to 5 double bonds. The prostaglandin is involved in adjustments of inflammation, pain, and swelling, adjustments of a blood pressure function, a cardiac function, and a gastrointestinal function, adjustments of a digestive enzyme secretion, adjustments of a renal function, blood coagulation, platelet aggregation, an allergic reaction, neural transmission, production of various hormones, and the like.
As a prostaglandin E1 (PGE1) preparation, intravenous-injection fat emulsions have been developed (see JP-B-1-57094, JP-B-1-57096, and JP-A-2001-10958, for example). Some of these emulsions are commercially available.
However, commercially available PGE1 fat emulsions must be stored at a low temperature (e.g., 5° C. or less) while blocking light. The quality assurance period of such PGE1 fat emulsions is short (e.g., 5° C.×1 year) even if the PGE1 fat emulsions are stored at a low temperature. This is because PGE1 (active ingredient) is chemically unstable. For example, since PGE1 fat emulsions must be prevented from freezing during storage, strict temperature control is necessary when storing PGE1 fat emulsions at 5° C. Since commercially available PGE1 fat emulsions must be stored under strict temperature control, it is difficult to control the quality of PGE1 fat emulsions during storage. Various attempts have been made to improve the stability of PGE1 (see JP-B-8-18989 and JP-A-4-338333, for example). However, these attempts have failed in achieving a sufficient effect. Some documents disclose measures to improve the stability of fat emulsions (see JP-T-2005-500366 and WO2004/52354, for example). However, these documents are silent about prostaglandin fat emulsions.
In view of this situation, development of a prostaglandin fat emulsion that exhibits excellent stability of active ingredient (prostaglandin) and excellent emulsion stability has been desired.